In the operation of a bicycle the handlebar is often subjected to a blow from an external source, resulting in a twisting of the handlebar stem 6 with respect to the fork stem 2 with consequent mis-alignment of the handlebars with respect to the longitudinal axis and direction of movement of the bicycle, which may result in adverse effect on its safe operation. It is therefore the object of the invention to provide means for insuring that the clamping ring 20 will not move relatively to the steering fork stem 2 when the handlebars are subjected to such an undesired twisting force.